Tel Aviv — After pointing a finger at Iran and promising a harsh retaliation for a terrorist attack in Bulgaria that killed five Israeli tourists yesterday, Prime Minister Benjamin Netanyahu today revised his accusation and toned down his threats for revenge.

Speaking to reporters, Mr. Netanyahu said it was Hezbollah, acting as the "long arm" of Iran, that actually carried out the attack. And instead of a vague threat of a "strong retaliation," Mr. Netanyahu spoke of a protracted manhunt to exact revenge on those responsible.

The more muted response suggests that, rather than opting for a harsh and swift retaliatory strike as it has in the past, Israel will keep a low profile and seek revenge in covert hits over time to avoid destabilizing an already chaotic region in the present.

For months Israel has been warning that it will attack Iran if it believes that Tehran is about complete a nuclear weapon. Today Netanyahu used the Bulgaria attack to disparage Iran as a pariah that would endanger the world if allowed to obtain nuclear weapons.

Shlomo Brom, a fellow at the Tel Aviv University think tank Institute for National Security Studies, says an overt act of revenge would risk triggering a regional war, something that Israel wants to avoid right now. For now, Israel is deferring to US efforts to apply economic pressure through sanctions and negotiations with Iran. An attack would undermine the United States.

"There is one issue they are obsessed with and that is the Iranian nuclear program," he says. "Attacking Iran and attacking Hezbollah involves a major escalation, and the question is whether Israel wants a major escalation. I suspected that Israel doesn’t want a major escalation."

To be sure, Israel has a track record of ordering swift and harsh revenge strikes, which sometimes escalate in to prolonged confrontations.

A year ago, Israel immediately launched strikes on the Gaza Strip after a deadly cross-border ambush from Egypt that Israel blamed on Palestinians. Israel's response to Hezbollah's 2006 kidnapping of Israeli soldiers on the Israel-Lebanon border kicked off a several-week war with the militant group. And Israel’s 1982 invasion of Lebanon followed an assassination attempt on its London ambassador by a Palestinian Liberation Organization operative.

The difference is that this time, risking war means risking the possibility of missiles raining down on all of Israel.

But analysts don’t see this attack as a sufficient casus belli. Giora Eiland, a former general and Israeli national security adviser, said Israel should keep its handling of Iran’s nuclear program separate from how it responds to the Bulgaria attack. He suggested that Israel needs to focus on cooperating with Bulgarian authorities to track down the perpetrators.

An attack on the nuclear sites depends on different considerations. "The main question… is whether you can reach an understanding with the US, that an Israeli action against Tehran will be accepted positively," Mr. Eiland told Israel Army Radio.

Israel is expected to use covert actions to retaliate instead, as it is suspected of doing in the past. Israel is widely believed to be behind a string of assassinations of Iranian nuclear scientists and attacks on Iranian military sites in recent years.

In addition, former national security adviser Uzi Arad told Israel Radio today that Israel was behind the assassination of Hezbollah military commander Imad Mughniyah in 2008 – the first time any Israeli official has claimed responsibility for the attack. There has been speculation that the bus bombing was retaliation for Mr. Mughniyah's death – a claim Hezbollah denied today.

Gerald Steinberg, a political science professor at Bar Ilan University, says that Netanyahu has been very cautious about using force in general. The Israeli leader is likely to order a manhunt as the government did after the assassination of Israel’s delegation to the 1972 Olympic Games in Munich.

"The history of Israeli responses to terror attacks like this are a very slow and carefully measured response where the perpetrators are identified, and one by one they are found," he says. "The regional environment is extremely unstable, and Israel is not the focus at all. Israel does not want this terror attack to drag it back into the focus as the source of all the instability in the region."